Heretofore it has been generally conceded by those skilled in the art of solution mining of sylvinite deposits that only thick beds, in essentially flat deposits, could be solution mined economically. In prior solution mining, an oil blanket, air blanket or some other such material had to be maintained on the top of the solution mining liquid in the ore cavity in order to avoid dissolution of the salt (NaCl) layer above the ore being mined.
In prior solution mining techniques, the width of the cavity developed by one or a plurality of wells was limited by the stability of the cavity roof and the fact that as the active dissolution face moved farther from the inlet, the major portion of the unsaturated solution was farther removed from contact with the active dissolution area, and solution activity in relation to cavity size decreased.
Exemplary of the prior art technology is the method described in U.S. Pat. No. 3,341,252 (Dahms et al.) entitled "Solution Mining of Sloping Strata". In this patent the method involves drilling a plurality of bore holes spaced in both the directions of the dip and in the direction of the strike in a sloping stratum, and communication is developed among the bore holes in the direction of the strike, but intentionally avoided in the direction of the dip. The patented technique recognizes prior art knowledge that otherwise inert protective layers of nonsolvent material such as hydrocarbon oil would be required to prevent vertical extraction in the cavity.
In U.S. Pat. No. 3,442,553 (Kutz) entitled "Slurry Mining of Carnallite", a method is described for slurry mining of double salts with specific reference to carnallite, which contains potassium chloride and magnesium chloride. In order for the method to work, it is necessary to have a steeply sloping bed containing double salts which form incongruently saturated solutions. The less soluble salt (potassium chloride) is left as a slurry in the bottom of the cavity. The less soluble salt is then removed as a slurry entrained by a saturated or nearly saturated solution of the more soluble salt.